Method for direct reduction and upgrading of fine-grained refractory and earthy iron ores and slags

ABSTRACT

A method of upgrading relatively rich, fine-grained earthy hematite iron ores is provided. The iron ore, after suitable preparation, is reduced using a solid state reduction technique. As a result of the reduction process, the iron grains undergo size enhancement while the nonmetallic oxides are unreduced and remain as refractory oxide gangue. After completion of the reduction process, the enlarged malleable metallic iron grains are crushed in such a way as to cause the iron grains to fuse together, forming large, flat iron flakes. In order to achieve maximum flake size, the crushing system applies a relatively gradual pressing force rather than a rapid, impact type of force. As the large flakes are formed, the iron grains are liberated from the refractory oxide grains resulting in an increase in density. The crushing system causes non-iron oxide bonds to be broken, resulting in the formation of residual refractory particles generally with a grain size of less than 0.05 millimeters. The shape, size, density, and ferromagnetic differences between the iron flakes and the nonmetallic oxides are used to separate the iron from the nonmetallics. A variety of different separation techniques may be used, including screens, jigs, spirals, elutriation, cyclones, magnetic, and gravity separation. The combination of solid state reduction, mechanical working, and physical/electromagnetic separation enable consistent production of super concentrates of material with metallic iron contents exceeding 92% with less than 4% oxide gangue and an iron recovery of greater than 95%.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/056,183, filed Apr. 6, 1998 which is a continuation ofprovisional application No. 60/055,308, filed Aug. 4, 1997 which areincorporated by reference herein for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to a method of concentratingiron ore and, more particularly, to a method of upgrading fine-grainedearthy hematite iron ores.

In recent years, the percentage of steel being produced throughout theworld using electric arc furnaces has increased to approximately 30%.However, unlike some other steel manufacturing systems, electric arcfurnaces require relatively high grade ore in which the total ironconcentration is greater than 68% with an oxide gangue concentration ofless than 3%. Materials with oxide gangue concentrations much beyondthis level produce an excessive volume of slag and therefore areuneconomically feasible as charge material.

Numerous relatively high-grade iron ores with iron concentrations in therange of 60 to 65% are of an earthy nature. These ores, whichproliferate in Western Australia, the Middle East, and Africa, aretypically intimately associated with extremely fine grained silica andalumina of feldspathic origin. Unfortunately, due to the fine grainstructure associated with these ores, liberating the iron and achievingthe oxide contaminant levels required for electric arc furnace chargematerial is nearly impossible and is generally cost prohibitive.

Several different processes have been developed for recovering ironconcentrates from ore. U.S. Pat. No. 2,944,884 discloses a technique forproducing high iron concentrates from low grade ores such as taconite.In the disclosed technique, the low grade ore is first crushed to minus⅜ inch or finer. The crushed ore is then mixed with a reactive form ofcarbon such that the mixture contains at least 50% more carbon than thetheoretical quantity needed for complete reduction. The mixture is thenheated for a period of time between 18 and 21 hours at a temperature ofabout 870 to 1100° C. so that the iron becomes fully reduced andcarburized. The material is rapidly cooled so that the iron carbideparticles lose their malleability. The charge is then ground and thecarburized iron particles containing at least about 0.65% carbon aremagnetically separated from the gangue particles.

U.S. Pat. No. 2,986,460 discloses a direct reduction process in whichthe iron ore is mixed with a carbonaceous reducing agent and then heatedin a rotary kiln at temperatures of about 900° C. The material is thencooled under controlled conditions in a non-oxidizing environment. Thereduced iron is then separated from most of the gangue and compactedinto briquettes.

In a more recent advance, U.S. Pat. No. 4,416,688 discloses a techniquefor reducing high phosphorus iron ore. In the disclosed technique spongeiron produced by selective solid state reduction is ground using a ballmill. The hammering action of the ball mill causes the formation of ironflakes of approximately 0.01 to 0.1 millimeters in size along withfinely divided oxide gangue. Conventional concentration techniques areused to obtain iron flake powder concentrate. The carbon content of thesponge iron must be kept to a minimum, preferably below 0.10% and atleast below 0.25%. Besides placing restrictions on the carbon content,the ability of the disclosed process to obtain high iron concentrateswith low oxide contents is hampered by the size of the iron flakesformed by the ball mill. As a result, the efficiency and therefore thecost effectiveness of this approach is lower than desirable.

Therefore a cost effective technique for obtaining super concentratematerials with high iron concentrations and low oxide concentrationsfrom relatively rich, fine-grained iron ores is needed.

SUMMARY OF THE INVENTION

The present invention provides a method of upgrading relatively rich,fine-grained earthy hematite iron ores. The iron ore, after suitablepreparation, is reduced using any of a variety of direct reductiontechniques. For example, the ore may be subjected to a high temperaturereduction utilizing hydrogen as the reductant gas. As a result of thereduction process, the iron grains undergo size enhancement. Under thesame conditions the contaminant oxides of silica, alumina, apatite,lime, and magnesia are calcined, but unreduced, and remain as refractoryoxide gangue.

After completion of the reduction process, the enlarged malleablemetallic iron grains are crushed in such a way as to cause the irongrains to fuse together, forming large, flat iron flakes. In order toachieve maximum flake size, the crushing system applies a relativelygradual pressing force rather than a rapid, impact type of force. In oneembodiment of the invention, a roll crusher is used to create flakesgreater than 1.0 millimeter in size, and typically in the range of 3.0to 5.0 millimeters in size. As the large flakes are formed, the irongrains are liberated from the refractory oxide grains resulting in anincrease in density from about 4 to 5 grams per cubic centimeter toabout 6 to 7 grams per cubic centimeter. At the same time that themechanical working of the reduced iron by the crushing means causes thefusion of the iron grains into flat flakes, the fineness of the residualoxide grains increases.

The shape, size, density, and ferromagnetic differences between the ironflakes and the nonmetallic oxides facilitate separation of the iron. Avariety of different separation techniques may be used, includingscreens, jigs, spirals, elutriation, cyclones, magnetic, and gravityseparation. Final concentration and cleaning can be accomplished bylow-intensity magnetic separation of the ferromagnetic metal flakes fromthe nonmagnetic residual oxides.

In one embodiment of the invention, the crushed, reduced material isseparated using a mesh screen. The large particles, preferably thoseparticles having a size greater than 3.0 millimeters, undergo flashgrinding to further liberate the iron from the nonmetallic oxides. Thesmall particles, those passing through the screen, undergo a longerperiod of grinding, in the range of 20 to 90 minutes. The ironconcentrate is separated from the oxides using a low intensity magneticseparator.

The combination of solid state reduction, mechanical working, andphysical/electromagnetic separation enable consistent production ofsuper concentrates of material with metallic iron contents exceeding 92%with less than 5% oxide gangue and an iron recovery of greater than 95%.If optimized, this method can achieve an iron content of between 94% and98% with less than 2% oxide gangue.

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the remaining portions of thespecification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram illustrating the principal steps associatedwith the present invention;

FIG. 2 is an illustration of the cross-section of a roll crusher used tofuse the iron particles in the present invention;

FIG. 3 is a cross-sectional view of the surfaces of a pair of corrugatedrollers;

FIG. 4 is an illustration of a roller mill; and

FIG. 5 is an illustration of the jaw members of a jaw crusher.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

FIG. 1 is a flow diagram illustrating the present invention. After theiron ore is obtained (step 101), it undergoes direct reduction (step103). As discussed below in further detail, a variety of differentdirect or solid state reduction processes may be used with the presentinvention, each process placing specific constraints (e.g., size) on thematerial to be reduced. The principal criterion in selected a directreduction process is the associated costs. The costs are primarily dueto the costs of fuel for the reduction process (e.g., hydrogen versuscoal), the efficiency of the selected process, and the amount of orepreparation necessary prior to reduction.

After the ore has been reduced, it is mechanically worked with a crusherin order to fuse the iron grains together to form metal flakes (step105). In other words, crushing as used herein refers to a process ofenlarging iron grains, the resultant enlarged material being in the formof iron flakes. A major portion of the resultant flakes are larger than1.0 millimeter, typically in the range of 3.0 to 5.0 millimeters insize. At the same time that the mechanical working causes the fusion ofthe iron grains, the refractory oxide grains are ground to increasingfineness, typically less than 0.05 millimeters in size. The flake formof the metallic iron grains versus the cubic shape of the residual oxidegrains is extremely important for physical separation.

The iron flakes are separated by size using any of a variety of wellknown separation techniques (step 107). For example, the crushedmaterial may be passed through a separation screen, the screenseparating the material into coarse or large flakes 109 and a mixture offine flakes, refractory oxide grains, and unliberated refractoryoxide-metal grains 110. The crushed material may also be separated usingsuch techniques as air classification.

If the coarse grains 109 meet the requirements of the end user, forexample the desired oxide levels, they may be sent directly to the finalconcentrate 111. If coarse grains 109 do not meet these requirements,they are flash ground for a period of time generally less than 30minutes, and preferably less than 15 minutes (step 113). After grinding,the materials are separated using a magnetic separator to recover themetallic iron components and reject the non-magnetic oxide gangue (step115). The rejected material is sent to the tailings 117.

The fine material 110 is ground for a longer period of time, preferablybetween 20 and 90 minutes (step 119). The amount of time required forthis step is primarily based on the size of fine material 110 providedby separation step 107, the composition of the initial ore, and therequirements placed on the final product. After completion of grindingstep 119, the material is magnetically separated into final concentrate111 and tailings 117 (step 121).

The present invention is particularly beneficial in processingrelatively high grade iron ores that are intimately associated withextremely fine-grained silica and alumina of feldspathic origin.Examples of such high grade ores include goethite, limonite, maghemite,and hematites. The iron content in these ores is commonly in the rangeof 60 to 65% while the residual oxide gangue contents are in the rangeof 6 to 9% with a relatively low phosphorus content of at most 0.05%(i.e., 0.11% P₂O₅). Due to the fine grain structure as well as theintimate associate of the iron ore with the oxide gangue, traditionalconcentration techniques are economically unfeasible as well as unableto achieve the desired oxide concentrations in the final product.

Preferably, prior to direct reduction, the mined iron ore is processedby one or more crushers. After the size of the mined ore has beenreduced by the crushers, it is typically separated by size. Both theextent to which the mined ore must be reduced in size and the subsequentprocessing steps are dependent upon the intended type of directreduction. Direct reduction systems as well as the requirements placedon the material to be processed are well known by those of skill in theart.

In a typical direct reduction system, the iron ore is placed within akiln and reduced at a temperature below the melt temperature of the ironore. Although various types of kilns may be used, typically shaft kilnsare preferred over rotary kilns for the reduction of iron ore due totheir high capacity. The kiln may use either a solid reducing agent suchas coke, char, or anthracite coal, or a gaseous reducing agent such ashydrogen, carbon monoxide, or natural gas. The temperature of the kilnmust be sufficiently high to heat the iron ore to a point where it isreduced to iron and is malleable during the subsequent crushing process.Although reduction temperatures as low as about 700° C. may be used,preferably the reduction temperature is at least 1000° C., and morepreferably between 1050 and 1200° C.

During heating and calcination, the porosity of the earthy hematites isenhanced due to the release of water of hydration. The enhanced porosityof these materials in combination with their fine grain size leads to ahigh surface area for interaction with the reducing gases. Iron graingrowth occurs, especially in the presence of hydrogen, if there aremetallic grains in contact with active grain surfaces. As a consequence,metallization levels of 95 to 98% may be achieved by reducing suchmaterials with hydrogen. Under the same reducing conditions, the otheroxides of finely entrained grains of silica (SiO₂), alumina (Al₂O₃),apatite (Ca₃(PO₄)₂), lime (CaO), magnesia (MgO), and titania (TiO₂) areunreduced. However, generally during reduction there is relief of somegrain boundary stresses associated with these non-iron oxides, leadingto a lower fracture energy and an improved grindability. As a result,the unreduced oxides remain in the matrix of the metallic iron asdiscrete friable residual oxide grains.

In one type of direct reduction system appropriate for the relativelyhigh grade iron ores of the present invention, hydrogen gas is used athigh temperatures, preferably at temperatures of 900 to 1050° C. orgreater. A benefit of hydrogen gas reduction is the minimization of thecarburization of the iron during reduction, thereby avoiding theformation of iron carbide (Fe₃C). Iron carbide formation from solutionin metallic iron initiates at 0.2% carbon content and martensiteformation is a factor at contents as low as 0.5% carbon if themetallized reduced product is improperly quenched or cooled. Ironcarbide is formed up to a saturation of 6.7% carbon and is nonmagnetic,hard, dense, and friable even with controlled cooling. As a result, theiron carbide does not lend itself to the subsequent physical processingand mechanical separation operations. Accordingly, carbon levels shouldbe kept to a minimum regardless of the type of reduction system used.However, material with a carbon content exceeding 0.25% and up to alevel of at least 1.5% may still be used with the present invention.

An additional benefit of hydrogen as a reducing gas is its highreactivity, leading to an increase in reduction rate and a higher degreeof iron oxide metallization than achievable using carbon monoxide (CO)gas as the reducing gas. Maximizing metallization minimizes theformation of wustite (FeO) in the metallic iron grains, a material thatis neither magnetic nor malleable. As a result of its properties, thewustite does not form flakes in accordance with the present invention,but instead reports with the residual oxides. Furthermore since it isnonmagnetic, it is not separable from the other oxides using magneticseparation. Therefore the inclusion of wustite leads to a loss of ironyield during separation and concentration.

In at least one embodiment of the invention, the iron ore fines arecoated with fine limestone or lime powder to isolate the iron oxideparticles. Limestone (CaCO₃) or lime (CaO) tends to form a thin inertlayer on the surface of the iron oxide particle or preballed iron oxidefines. This inert layer helps to prevent granular fusion of theintermediate low melting temperature iron oxide phase (FeO) andconcomitant clustering during reduction. The limestone/lime coating alsoprevents stickiness of the iron oxide fines at elevated temperatures,thereby allowing an increase in the processing temperature above therange of 900° to 1000° C.

Another aspect of at least one embodiment of the invention relates topreballing of the iron ore fines to minimize ultrafines in the feed tothe fluid bed or hearth prior to reduction roasting. If there is anexcess of ultrafine micron size material in the reduction feed, it canbecome gas borne and flash out of the roaster with insufficient contacttime for a high degree of reduction. Preballing of the reduction roasteriron oxide feed with a water spray will adhere the fines particles tothe surfaces of the coarser particles basically eliminating the slimesfraction in the reduction furnace feed. As a result, a more consistentand uniform metallization can be achieved. Preballing of earthyhematites works particularly well due to the slimes nature of the ironoxides, generally not even requiring a binder.

Even if hydrogen gas is used as the reductant in the reduction system,the output of the reduction furnace can be enhanced with the addition offine carbon, typically in the form of pulverized coal or coke. The solidfuel (i.e., coal or coke) is pulverized to finer than 0.07 millimetersand is mixed with the iron oxide fines. If a preballing step such asthat described above is included in the process, the pulverized solidfuel can be blended during this step. When the solid fuel in intimatecontact with the iron oxide is heated, it acts as a powerful reductant,increasing the rate of oxygen removal. If the carbon in the solid fuelis applied at less than stoichiometric quantities, such that there islittle, if any, carbon excess, there is no problem with carbon solutionin the iron and iron carbide formation.

After the iron ore has undergone direct reduction, the resultant spongeiron is cooled under a controlled environment, preferably in anon-oxidizing atmosphere. The sponge iron is then crushed in such a wayas to cause the malleable iron grains to fuse together to form largeiron flakes. Although a variety of crushing techniques may be used inaccordance with the invention, a common attribute of these techniques isthat a relatively gradual pressing force is applied to the materialrather than a rapid, impact type of force. A roll crusher is an exampleof a mechanism that applies a force in accordance with the presentinvention while the hammering action of a ball mill is an example of animpact force system.

During the crushing step of the present invention, metallic iron grainsare liberated from the refractory oxide grains. As the crushing stepcontinues, the malleable iron grains become fused together to formlarge, substantially flat flakes. Thus as opposed to reducing the sizeof the grains as is typical of a crushing operation, the iron grains aresubstantially enlarged through the fusion process. At the same time, thecrushing step causes non-iron oxide bonds to be broken, both at grainboundaries and across grains. As a result, residual refractory particlesare formed, typically with a grain size of less than 0.05 millimetersand generally less than 0.01 millimeters.

A substantial portion of the discrete iron flakes formed by the crushingstep of the present invention are greater than 1.0 millimeter in size,and are typically in the range of about 3.0 to 5.0 millimeters. Thus thecrushing step of the present invention leads to an increase in grainsize by a factor of up to 500, assuming an initial grain size of 0.01millimeters. Furthermore, as the iron grains are liberated from therefractory oxide grains, the density of the resultant iron grains isincreased from about 4 to 5 grams per cubic centimeter to about 6 to 7grams per cubic centimeter. As a result there is a major differencebetween the specific gravity of the metal flakes and the residualoxides.

In addition to the basic refractory oxides and soft metal grains passingthrough the crushing mechanism, there are also hybrids of refractoryoxide-metal grains. In some instances these hybrid grains are simply dueto the non-liberation of the iron grains from the refractory oxidegrains, a condition that may be remedied through further crushing. Inother instances the hybrid grains are metal grains that are embeddedwith refractory particles or, perhaps, metal grains smeared onto largerrefractory particles. The two latter hybrids are undesirable as theylead to a lowering of iron yield. Therefore it is imperative that therefractory grains are flushed or elutriated by a fluid from the metalgrains as rapidly as they are liberated thereby minimizing contaminationthrough excessive contact of the refractory oxides and the metal grainsduring the crushing step.

In order to flush liberated refractory grains during the crushing step,in at least one embodiment of the invention the crushing mechanismincludes a fluid. The fluid can be water, air, gas, or some othermedium.

In the preferred embodiment of the invention, a roll crusher is usedduring the flake formation step. FIG. 2 is an illustration of thecross-section of a roll crusher 200. Roll crusher 200 is comprised totwo rollers 201 and 203 rotating in opposite directions 205 and 207,respectively. Material 209 from the direct reduction system is fed alonga direction 211. As the material passes between rollers 201 and 203, itis gradually pressed between the rollers and crushed. The outputmaterial 213 is comprised of fusion formed iron flakes, crushed non-ironoxides, and some hybrid material as described above. At this pointoutput material 213 may be separated or run through roll crusher 200 oneor more additional times. Alternatively, material 213 may be separatedand only a portion of the material returned to crusher system 200 foradditional pressing.

Although both rollers of roll crusher 200 may be rigidly mounted,preferably one or both rollers are spring rollers. In a rigid mountedsystem in which both rollers are rigidly coupled to a frame, if anuncrushable particle enters the rollers or if too much material entersthe rollers at one time, the rollers will either stall or the crusherwill experience some type of mechanical failure. These problems arealleviated with the spring roller system which allows the separationdistance between the rollers to expand under these conditions.

In the preferred embodiment of the invention, rollers 201 and 203 have adiameter of 91.44 centimeters each. Other diameters may also be usedwith the present invention, the diameters being selected using wellknown formulas based on such factors as the size of particles 209, thenip angle, and the distance separating the rollers. For the preferredembodiment of the invention, the distance separating the rollers isnominally 0 (i.e., the roller surfaces are in contact). The principalfactor in determining the length of rollers 201 and 203 is the desiredthroughput. Utilizing this embodiment of the invention, at least 20% ofthe iron flakes from crusher 200 are 1.0 millimeter or greater.Typically in this embodiment between 20% and 50% of the iron flakes arebetween 3.0 and 5.0 millimeters in size. The residual refractoryparticles passing through the crusher generally have a grain size ofless than 0.05 millimeters and typically less than 0.01 millimeters.

In an alternate embodiment of the invention, the surfaces of the rollersof roll crusher 200 have mating, corrugated surfaces. FIG. 3 is across-sectional view of the roller surfaces of this embodiment takenalong the centerline of the rollers. Rollers 301 and 303 have corrugatedsurfaces 305 and 307, respectively. The benefit of the corrugatedsurfaces is an increase in the crushing surface of the rollers, thusproviding higher material throughput than flat rollers of a similarlength 309.

In an alternative embodiment of the invention, roll crusher 200 isreplaced with a roller mill. A roller mill crushes material in a similarfashion to that of a roll crusher, gradually applying mechanicalpressure to the material. There are a variety of types of roller millswell known by those of skill in the art. For example, a roller mill maybe vertical or horizontal and the pressure forcing the roller surfacestogether may be induced by gravity, springs, centrifugal force, or somecombination thereof. Typically this type of mill includes one largemetal ring within which one or more smaller metal rings roll. Forexample, a roller mill 400 is shown in FIG. 4. Mill 400 includes onelarge, metal, floating ring 401 against the inside surface of which arepressed three smaller rings 403-405. Typically only ring 403 is driven,causing floating ring 401 to rotate as well as small rings 404 and 405.Material is crushed as it passes between the inner surface of ring 401and the outer surfaces of rings 403-405.

In an alternative embodiment of the invention, a jaw crusher is used tocrush the material reduced in the direct reduction system. The jawcrusher utilizes two crushing surfaces, 501 and 503, as illustrated inFIG. 5. Surface 501 is fixed while surface 503 is movable. In use, jaw503 alternately approaches and recedes from surface 501, crushingmaterial 505 as it passes through the jaws. The surfaces of jaws 501 and503 may be flat or one or both surfaces of the jaws may be corrugated orcurved.

The present invention is not limited to the crushing mechanismsdescribed above, rather other types of crushers may be used with similarresults. However, the selected crusher must impart a graduallyincreasing pressure on the material rather than a rapid, impact type ofpressure, resulting in a major portion of the iron flakes being greaterthan 1.0 millimeter in size, and preferably greater than 3.0 millimetersin size. Typically, the selected crusher is chosen on the basis of bothperformance and operating costs. For example, there are a variety ofroller mills that impart sufficient, gradual pressure to the reducedmaterial to crush the non-iron oxides while fusing the iron particlesinto large flakes. However, many of these roller mills are not suitablebased on their operating costs.

After the reduced material has been sufficiently crushed to form largeiron flakes, it is separated using conventional separation techniques.These techniques may be based on particle size, shape, or density. Forexample, in the preferred embodiment a 20 mesh screen (i.e., 0.813millimeter aperture) is used to separate the material into coarsematerial and fine material. Other mesh sizes, for example screens withsmaller apertures, may be used with the present invention. However, oneadvantage of the 20 mesh screen is that in many instances the largeparticles contain a sufficiently high percentage of iron and asufficiently low percentage of non-iron oxides to be immediately usedwithout undergoing further separation.

Besides screen separating, other techniques such as jigs, spirals,elutriation, cyclones, and gravity separators may be applied to thecrushed material to separate the iron flakes from the fine residualoxide grains. In addition, the flat form of the metal flakes allowsapplication of surfaces, such as spirals or cones, in the presence offluids, for metal separation as the flake particles will cling to theflat surfaces while the cubic shaped refractory particles will beflushed away.

After the large flakes have been separated from the smaller flakes andthe non-iron oxide particles, the large flakes are either sent directlyto the final concentrate or undergo further oxide elimination. Iffurther oxide elimination is required, the coarse material is firstsubjected to a flash grind, typically in the range of 5 to 30 minutes ofgrinding, and preferably in the range of 5 to 15 minutes. Aftergrinding, the iron flakes are removed from the non-iron oxides,preferably using a magnetic separator. Similarly, in the preferredembodiment the fine material exiting the initial separation stage isfirst ground and then magnetically separated into final product andtailings. The grinding step for the fine material lasts between 20 and90 minutes, and preferably less than 60 minutes. The magnetic separatoruses a low intensity magnetic field to recover the metallic ironcomponents and reject the non-magnetic oxide gangue.

Typically, once the material is properly separated into finalconcentrate and tailings, the tailings are sent to waste disposal whilethe concentrate is dried using conventional means. Preferably the dryingoperation takes place under controlled environmental conditions, thusavoiding oxidation of the iron particles.

After the concentrate has been suitably dried, it may be formed intobriquettes using any of a variety of conventional techniques. In thepreferred embodiment a fine mist of oil or lubricant is used to improvethe packing density of the metal powder briquettes. The mist is appliedafter drying and before briquetting. The oil spray provides a lubricantat the powder surfaces, thus allowing the particles to slip on eachother in the briquetting press, thereby improving briquette strength.The oil spray also minimizes the electrostatic charge on the metalparticles acquired during drying. Since the electrostatic charge tendsto reduce particle packing, minimization of the charge improves theachievable packing density.

EXAMPLES

The method of the present invention was evaluated on high grade iron orefrom Marra Mamba of Western Australia. This ore contained 62% Fe, 3.7%SiO₂, 2.2% Al₂O₃, and 0.052% P. Due to the intimate association of theiron with extremely fine grained silica and alumina, separation andbeneficiation of the iron grains using conventional techniques isimpractical.

The ore was reduced at a temperature of 1025° C. for 1.5 hours using 40%PUC coal. Chemical analyses of the direct reduced material prior tocrushing and separation, averaged over six samples, yield ametallization of 91.19% with 78.24% iron, 8.18% SiO₂, 2.992% Al₂O₃,0.041% P, and 5.81% C.

After direct reduction, the material was roll crushed using a springtensioned, 30 centimeter diameter roll crusher. The crushed material wasseparated with a 20 mesh screen. In the following sample, the materialpassing through the screen (i.e., <20 mesh) was subjected to a 90 minutegrind while the material that did not pass through the screen (i.e., >20mesh) was subjected to a 15 minute grind. Chemical analysis of theresults yields:

Wt Rec Wt Rec_(Fe) Fe_(tot) Description (%) (%) (%) SiO₂ (%) Al₂O₃ (%) P(%) Conc 85.23 95.48 93.31 2.21 1.146 0.019 Tail 14.77 3.77 25.51 32.4913.644 0.166 Head 100.00 100.00 83.30 6.68 2.992 0.041

Thus the iron content was increased from 83.30% to 93.31% at a 95.5%iron recovery. Silica and alumina oxides were reduced from 9.67% to3.36% while the phosphorus concentration was halved from 0.041% to0.019%.

As will be understood by those familiar with the art, the presentinvention may be embodied in other specific forms without departing fromthe spirit or essential characteristics thereof. For example, a varietyof different separation techniques may be used. Furthermore, theinvention is not restricted to a single method of direct reduction noris it restricted to a single method of crushing the reduced materials.Accordingly, the disclosures and descriptions herein are intended to beillustrative, but not limiting, of the scope of the invention which isset forth in the following claims.

What is claimed is:
 1. A method for obtaining an iron concentrate from acharge of iron ore, the method comprising the steps of: reducing saidcharge of iron ore with a direct reduction process to obtain a reducediron material; crushing said reduced iron material to form a pluralityof iron flakes and a plurality of refractory particles, wherein asubstantial portion of said plurality of iron flakes are greater than1.0 millimeter in size and wherein a substantial portion of saidplurality of refractory particles are smaller than 0.05 millimeters insize; and separating said crushed material to obtain said ironconcentrate.
 2. The method of claim 1, wherein said direct reductionprocess operates at a temperature of at least 700° C.
 3. The method ofclaim 1, wherein said direct reduction process operates at a temperatureof at least 1000° C.
 4. The method of claim 3, wherein said temperatureis between about 1050° C. and 1200° C.
 5. The method of claim 1, whereinsaid direct reduction process uses at least one gaseous reductant. 6.The method of claim 5, wherein said at least one gaseous reductant ishydrogen.
 7. The method of claim 5, wherein said at least one gaseousreductant is a mixture of hydrogen and carbon monoxide.
 8. The method ofclaim 1, wherein said direct reduction process uses a solid reducingagent.
 9. The method of claim 8, wherein said solid reducing agent isselected from the group consisting of coke, char, and anthracite coal.10. The method of claim 1, further comprising the step of coating saidcharge of iron with a calcium containing material prior to said reducingstep, wherein said calcium containing material is selected from thegroup consisting of limestone and lime.
 11. The method of claim 1,further comprising the step of preballing said charge of iron prior tosaid reducing step.
 12. The method of claim 11, further comprising thestep of blending pulverized solid fuel to said preballed charge of iron.13. The method of claim 12, wherein said pulverized solid fuel isselected from the group consisting of coal or coke.
 14. The method ofclaim 13, wherein said pulverized solid fuel is pulverized to finer than0.070 millimeters in size.
 15. The method of claim 12, wherein saidblending step occurs prior to said preballing step.
 16. The method ofclaim 1, further comprising the step of cooling said reduced ironmaterial in a non-oxidizing atmosphere prior to said crushing step. 17.The method of claim 1, wherein said substantial portion of saidplurality of iron flakes is at least 20% of said plurality of ironflakes.
 18. The method of claim 1, wherein at least 20% of saidplurality of iron flakes are greater than 3.0 millimeters in size. 19.The method of claim 1, wherein said crushing step utilizes a rollcrusher.
 20. The method of claim 19, wherein said roll crusher furthercomprises a pair of rollers, each of said rollers having a corrugatedsurface.
 21. The method of claim 1, wherein said crushing step utilizesa roller mill.
 22. The method of claim 1, wherein said crushing steputilizes a jaw crusher.
 23. The method of claim 1, said separating stepfurther comprising the steps of: screening said crushed material into acoarse material and a fine material; grinding said fine material; andmagnetically separating iron concentrates from said coarse material andsaid fine material.
 24. The method of claim 23, further comprising thestep of grinding said coarse material.
 25. The method of claim 23,wherein said grinding step lasts for a period of time between about 20minutes and about 90 minutes.
 26. The method of claim 24, wherein saidgrinding step for said coarse material lasts for a period of timebetween about 5 minutes and about 30 minutes.
 27. The method of claim23, wherein said screening step uses a 20 mesh screen.
 28. The method ofclaim 1, further comprising the step of briquetting said ironconcentrate.
 29. The method of claim 28, further comprising the steps ofdrying said iron concentrate and spraying said dried concentrate with anoil spray prior to said briquetting step.
 30. The method of claim 1,wherein said iron concentrate contains greater than 92% iron and lessthan 5% silica and alumina oxides.
 31. The method of claim 1, whereinsaid iron concentrate contains greater than 95% iron and less than 2%silica and alumina oxides.
 32. A method for obtaining an ironconcentrate from a charge of iron ore, the method comprising the stepsof: reducing said charge of iron ore with a direct reduction process toobtain a reduced metallic iron material; crushing said reduced metalliciron material with a roll crusher to form a plurality of iron flakes anda plurality of refractory particles, wherein a substantial portion ofsaid plurality of iron flakes are greater than 1.0 millimeter in sizeand wherein a substantial portion of said plurality of refractoryparticles are smaller than 0.05 millimeters in size; separating saidcrushed material into a coarse material and a fine material; grindingsaid fine material; separating said iron concentrate from said coarsematerial and said ground fine material.
 33. The method of claim 32,further comprising the step of grinding said coarse material, whereinsaid coarse grinding step is prior to said iron concentrate separatingstep.
 34. A method for obtaining an iron concentrate from a charge ofiron ore, the method comprising the steps of: reducing said charge ofiron ore with a direct reduction process to obtain a reduced metalliciron material, wherein said direct reduction process uses at least onegaseous reductant, wherein said at least one gaseous reductant includesa hydrogen gas; crushing said reduced metallic iron material with a rollcrusher to form a plurality of iron flakes and a plurality of refractoryparticles, wherein at least 20% of said plurality of iron flakes aregreater than 3.0 millimeters in size; screening said crushed materialinto a coarse material and a fine material; grinding said fine material;and separating said iron concentrate from said coarse material and saidground fine material, wherein said iron concentrate contains greaterthan 95% iron and less than 2% silica and alumina oxides.
 35. The methodof claim 34, wherein a substantial portion of said plurality of ironflakes are greater than 1.0 millimeter in size.
 36. The method of claim35, wherein a substantial portion of said plurality of refractoryparticles are smaller than 0.05 millimeter in size.
 37. The method ofclaim 34, wherein a substantial portion of said plurality of refractoryparticles are smaller than 0.05 millimeter in size.